This invention relates generally to linkages for construction machinery and more particularly to stops for stopping rack back movement of an implement.
Wheel loaders and track loaders have linkages for pivoting a bucket between a loading position, a transporting position and a dumping position. In a loading operation, a bucket is driven into the material being loaded and the bucket is pivoted to a rolled back or racked back position against a pair of rack stops. The rack stops are engaged by the bucket or a bucket tilt linkage. The impact of the engagement of the rack stops, particularly with a loaded bucket, places considerable stress on the rack stops and on the components carrying the rack stops. With the increasing load capacity of loader buckets, some with over 30 cubic meter capacity, the rack stops, the linkage and the components supporting the rack stops are being subjected to increasingly greater impacts and stresses. The impacts result in deformation of the rack stops and structural damage to the components carrying the rack stops. In loader linkages having a rack stop located at an intermediate point on a link, it has been found necessary to increase the cross section of the link in order to withstand the bending stress imposed on the link when the rack stop is engaged. This increases the cost and weight carried by the lift cylinder and results in a reduction in machine payload. In some loaders, the rack stops are located in the primary load paths of the structure and thus the impact on the rack stops undesirably increases the stress in that part of the component. This results in additional structural members being added to withstand the stress. Again, the weight and cost are increased and the payload capacity is decreased. In the design of a loader linkage, it is desirable to have gradual changes of direction in the structure to avoid points of stress concentration. Some prior loaders have incorporated rack stops in a manner that results in some highly stressed points in the structure.
U.S. Pat. No. 4,768,917 issued Sep. 6, 1988 to Anthony L. Garman for Loader Boom Mechanism discloses a loader linkage. A single bucket tilt link has a rack stop beneath its bucket connecting end which abuts a rack stop in the form of a large reinforced projection on the top wall of a hollow boom. The projection is laterally centered on the top wall of the boom and above a pivot connection between the boom and the bottom end of a tilt lever. The rack stop on the boom is in a primary stress path in the top wall of the boom and therefore the rack back impact on the rack stop detrimentally increases the stress in a top wall and may result in a deformation.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, rack stops are positioned on a loader boom remote from the primary load paths of the boom, thus avoiding the need to add additional structure to the boom to withstand the additional stress in the primary load paths. This minimizes cost of material and maximizes payload capacity. In another aspect of the present invention, the rack stops on the tilt links have abutment surfaces which are normal to the pivot pins connecting the tilt links to the upright tilt levers. The rack back impact force is passed in compression through the ends of the tilt links directly to the pins without subjecting the tilt link to bending stress. This avoids the necessity of adding structure, and weight, to the tilt links to withstand the additional stress imposed on the tilt links if the rack back force were not passed directly to the pivot pins.